A resident of the suburb was standing just a few meters from where the body fell at around 5 a.m. on Thursday, said Niger Interior Minister Abdou Labo.
"The police discovered the lifeless body of a black person lying in blood," Labo said, adding that blood had also been spotted on the left wing of the plane.
Initial information indicated the body was that of a stowaway who fell from the landing gear, said an Air France spokesman, Christophe Paumier, in Paris.
Paumier said the investigation was in the hands of authorities in Niamey.
The plane was coming from Burkina Faso's capital, Ouagadougou, and was scheduled to continue to Paris, Labo said.
Officials were holding the plane in Niamey so crew members and passengers could be interviewed, and investigators in Ouagadougou were also looking into "the conditions in which the passengers boarded," Labo said.
"At the moment, the plane is grounded on the tarmac at the airport and the flight to Paris is canceled until the end of the investigation," he said.
Passengers were being rerouted to Paris on two flights due to land in Paris Friday morning, Paumier said.
Associated Press writer Elaine Ganley contributed reporting from Paris.